001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      https://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.validator.routines.checkdigit;
018
019/**
020 * International Standard Serial Number (ISSN)
021 * is an eight-digit serial number used to
022 * uniquely identify a serial publication.
023 * <pre>
024 * The format is:
025 *
026 * ISSN dddd-dddC
027 * where:
028 * d = decimal digit (0-9)
029 * C = checksum (0-9 or X)
030 *
031 * The checksum is formed by adding the first 7 digits multiplied by
032 * the position in the entire number (counting from the right).
033 * For example, abcd-efg would be 8a + 7b + 6c + 5d + 4e +3f +2g.
034 * The check digit is modulus 11, where the value 10 is represented by 'X'
035 * For example:
036 * ISSN 0317-8471
037 * ISSN 1050-124X
038 * </pre>
039 * <p>
040 * <strong>Note:</strong> This class expects the input to be numeric only,
041 * with all formatting removed.
042 * For example:
043 * </p>
044 * <pre>
045 * 03178471
046 * 1050124X
047 * </pre>
048 *
049 * @since 1.5.0
050 */
051public final class ISSNCheckDigit extends ModulusCheckDigit {
052
053    private static final long serialVersionUID = 1L;
054
055    /** An ISSN is exactly eight characters: seven digits plus the check digit. */
056    private static final int ISSN_LEN = 8;
057
058    /**
059     * Singleton ISSN Check Digit instance.
060     */
061    public static final CheckDigit ISSN_CHECK_DIGIT = new ISSNCheckDigit();
062
063    /**
064     * Creates the instance using a checkdigit modulus of 11.
065     */
066    public ISSNCheckDigit() {
067        super(MODULUS_11);
068    }
069
070    /**
071     * {@inheritDoc}
072     *
073     * <p>
074     * The {@code 9 - leftPos} weighting gives a ninth character a weight of zero, so an over-length code left the
075     * trailing characters unweighted and still passed the modulus test (for example every {@code 03178471} + digit
076     * validated). The length is checked here so only a genuine eight-character ISSN reaches the check digit test.
077     * </p>
078     */
079    @Override
080    public boolean isValid(final String code) {
081        return isLength(code, ISSN_LEN) && super.isValid(code);
082    }
083
084    @Override
085    protected String toCheckDigit(final int charValue) throws CheckDigitException {
086        if (charValue == 10) { // CHECKSTYLE IGNORE MagicNumber
087            return "X";
088        }
089        return super.toCheckDigit(charValue);
090    }
091
092    @Override
093    protected int toInt(final char character, final int leftPos, final int rightPos)
094            throws CheckDigitException {
095        if (rightPos == 1 && character == 'X') {
096            return 10; // CHECKSTYLE IGNORE MagicNumber
097        }
098        return super.toInt(character, leftPos, rightPos);
099    }
100
101    @Override
102    protected int weightedValue(final int charValue, final int leftPos, final int rightPos) throws CheckDigitException {
103        return charValue * (9 - leftPos); // CHECKSTYLE IGNORE MagicNumber
104    }
105}